And now, a firsthand account of the emergency response to the attacks. We're going to hear from a Boston doctor who spoke with our co-host Audie Cornish.

AUDIE CORNISH, HOST:

Joining us now is Dr. Michael Gibson. He's a professor of medicine at Harvard Medical School. He's been seeing the victims of today's explosions in Boston in the emergency room at Beth Israel Deaconess Medical Center. Dr. Gibson, to begin, what kind of injuries are you seeing? What's coming into the emergency room there?

DR. MICHAEL GIBSON: Well, these are what are generally called battlefield injuries. What you see often with explosive devices are these lower extremity injuries. And there are a lot of those in the emergency room, frankly, everything from extensive shrapnel all the way to actually what is called traumatic amputation where a limb is missing from the victim.

CORNISH: And you were off duty, I hear, at the time that this happened. Tell us about how you learned about the explosions and how you were called in to help.

GIBSON: Well, I was - actually, I was working, and my son who ran the marathon, he's a Harvard medical student, texted me at 2:54 and said, I'm OK. And I wrote back, well, you must be sore, but then he wrote back, no, there's been an explosion. And at that point, I looked on Twitter and began to see what was happening and went down to the emergency room to get ready. I was the cardiologist here on call, and myself, trauma surgeons, orthopedic surgeons and everyone went to the emergency room.

And I - what I learned is that it's very important to be organized in triage. A lot of people arrived on the scene, but the crew was very, very effective there in getting everyone in the right spot for the right patients.

CORNISH: And as people were coming in, I hear that people were helping each other, trying to do kind of tourniquets in the field. What kinds of things did you see along those lines?

GIBSON: I was amazingly impressed with how stable the patients were as they arrived. I mean, the team in the field did a great job. I think having the injury tent right at the finish line may have saved innumerable lives.

CORNISH: So it wasn't just kind of citizens helping each other out. The emergency tent was right there.

GIBSON: Yeah. We're very lucky to have had the emergency tent right there.

CORNISH: Now, what, if any, security concerns are there at the hospital?

GIBSON: Well, right now, we are in complete lockdown. And I exited the hospital to come over and get on my phone, so I'd have a better reception with you. And it was hard for me to get back into the hospital. I had to undergo a pat down. I had to use all of my credentials to get back in. So, I, you know, I would advise no one to come to the hospital unless they're a patient, unless they're a caregiver, unless they're a family member.

There's police who've cordoned off all the entrances, and there's military people. It's very secure here at this point.

CORNISH: Dr. Michael Gibson, thank you so much for speaking with us.

GIBSON: My pleasure.

CORNISH: That's Dr. Michael Gibson. He's a professor of medicine at Harvard Medical School. He has also been working today in the emergency room at Beth Israel Deaconess Medical Center in Boston.

ROBERT SIEGEL, HOST:

And that is our colleague Audie Cornish. At last check, by the way, Beth Israel Deaconess had close to 20 patients from the race.

BLOCK: And to recap: Three people were killed today, more than 100 injured in two explosions at the finish line of the Boston Marathon. The White House is treating the incident as an act of terrorism.

SIEGEL: Earlier this evening, shortly after 6 p.m., President Obama made a statement from the White House, and he said this: We will find out who did this. He added, any responsible individuals, any responsible groups will feel the full weight of justice.

BLOCK: And we'll be continuing to update this story throughout the program and at npr.org. Transcript provided by NPR, Copyright NPR.